In our earlier work, we compared the global expression profiles of mouse ES cells and trophoblast stem (TS) cells by DNA microarrays. We studied Esg1, one of the genes identified as a gene expressed specifically in ES cells, and found that the gene encodes an RNA-binding protein that binds to many RNA targets. We have also compared the expression profiles of mouse ES cells undergoing neural differentiation in vitro and those of adult neural stemprogenitor (NS) cells. The results suggested that ES cells undergoing neural differentiation in vitro recapitulate the development of neural lineages in vivo. We also found a set of 4,000 genes, the expression of which increased with neural commitmentdifferentiation and can be used as a scale for the degree of commitmentdifferentiation in neural differentiation. We are extending these studies by carrying out global gene expression profiling of mouse embryonic germ (EG) cells and multipotent adult stem cells (MAPCs).